The venerable make program comes in many flavors. It has numerous quirks.
And it offers only a very restricted interface. Yet it remains an important
tool for organizing project builds, deploys, and other operations.
If you use make in your projects, chances are that you use gmake. Here are
some useful tricks to use with gmake.
Which make?
Do you work on a system where make is not gmake? If you inadvertently
invoke make, do you get a long list of syntax errors? Some versions of
make use a .BEGIN target that executes before anything else, and that
gmake sees as an ordinary target. So adding the following target at the end
of your Makefile alerts you to the use of the wrong version of make.
.BEGIN:
@echo "This Makefile requires gmake"; exit 1
Help by Default
The default target in gmake is the first target in the Makefile. A help
target is a good choice for that position. It is a safe, because it merely
informs without taking potentially dangerous actions. And it encourages the
good practice of documenting all targets in the Makefile. The define and
info directives make it easy to write multiline help.
define help_text :=
help:
Print this message
Some more generic help for using this Makefile.
target:
Documentation for target.
endef
help:
@$(info $(help_text))
Confirmations
What if you call gmake from the command line, sometimes under unusual
conditions, and in those cases you want to confirm whether to proceed? Use one
of these targets as a prerequisite for any recipe that requires confirmation
before execution.
Simple Confirmation
Continue if the answer is ‘yes’ and stop otherwise.
confirm:
@printf "Continue? [yes|No] " && \
read answer && test 'yes' = "$$answer" && exit 0 || exit 1
Process ID Confirmation
Continue if the answer is ‘yes’ plus the process ID and stop otherwise. Functionally the same as simple confirmation, it requires more engagement from the caller.
confirm-pid:
@r="$$$$" && \
printf "Continue? [yes-$$r|No]: " && \
read answer && test "yes-$$r" = "$$answer" && exit 0 || exit 1
Git Branch Confirm
Confirm that you are on the intended branch in git. Proceed if the current
branch matches the required branch name, otherwise confirm before proceeding.
confirm-git-branch-%:
@test '$*' = "`git branch --show-current`" && exit 0 || { \
printf "Current branch '`git branch --show-current`' is not '$*'. Continue? [yes|No] " && \
read answer && test 'yes' = "$$answer" && exit 0 || exit 1; \
}
Required Environment Variables
This recipe fails if an environment variable is either unset or empty. Use it as a prerequisite in a recipe that relies on an environment variable.
require-env.%:
@test "X$($*)" != "X" && exit 0 || { \
echo 'Environment variable not set: $*' && exit 1; \
}
Useful Options
By default, gmake announces every change of directory. These outputs may
interfere with pipelines in recipes, or clutter the otherwise useful output of
your gmake run. To avoid this, use the following variable setting.
MAKEFLAGS += --no-print-directory
Does your project use the vast array of builtin rules and variables that support them? It doesn’t? Then turn them off.
MAKEFLAGS += -r -R
Further Reading
John Graham-Cumming has written numerous
articles
detailing tricks and troubles with gmake. He also authored The GNU Make
Book, and the GNU Make Standard
Library.